Flexible process for enhancing steam cracker and platforming feedstocks

ABSTRACT

A process for increasing the yields of light olefins or shifting to increase the hydrocarbon components to gasoline blending pools from a hydrocarbon feedstock is presented. The process includes separating a naphtha feedstock to components to a first stream that are more readily processed in a cracking unit and to components in a second stream that are more readily processed in a reforming unit. The process includes the ability to convert components from the cracking stream to the reforming stream, and to convert components from the reforming stream to the cracking stream.

CROSS REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Application No. 61/863,019 filed on Aug. 7, 2013.

FIELD OF THE INVENTION

The present invention relates to a process and system for the production of aromatics from a heavier hydrocarbon stream. In particular, this process provides for increasing yields and flexibility of the production of aromatics and light olefins from hydrocarbon feedstock.

BACKGROUND

The reforming of petroleum raw materials is an important process for producing useful products. One important process is the separation and upgrading of hydrocarbons for a motor fuel, such as producing a naphtha feedstream and upgrading the octane value of the naphtha in the production of gasoline. However, hydrocarbon feedstreams from a raw petroleum source include the production of useful chemical precursors for use in the production of plastics, detergents and other products.

The upgrading of gasoline is an important process, and improvements for the conversion of naphtha feedstreams to increase the octane number have been presented in U.S. Pat. Nos. 3,729,409; 3,753,891; 3,767,568; 4,839,024; 4,882,040; and 5,242,576. These processes involve a variety of means to enhance octane number, and particularly for enhancing the aromatic content of gasoline.

Processes include splitting feeds and operating several reformers using different catalysts, such as a monometallic catalyst or a non-acidic catalyst for lower boiling point hydrocarbons and bi-metallic catalysts for higher boiling point hydrocarbons. Other improvements include new catalysts, as presented in U.S. Pat. Nos. 4,677,094; 6,809,061; and 7,799,729. However, there are limits to the methods and catalysts presented in these patents, and which can entail significant increases in cost.

Light olefins have traditionally been produced through the process of steam or catalytic cracking, and comprise ethylene and propylene. Light olefins are also derived from the same feedstocks as gasoline. Because of the limited availability and high cost of petroleum sources, the cost of producing light olefins from such petroleum sources has been steadily increasing. The ability to shift components in the feedstock for light olefins and gasoline pools enables producers to economically choose the most important product line and to shift some of the hydrocarbon components in an efficient manner.

SUMMARY

A process for improving yields of light olefins, reformate, and providing flexibility in the processing of a naphtha feed is presented. A first embodiment of the invention is a process to increase light olefin and reformate yields, comprising passing a first portion of a hydrocarbon feedstream to a fractionation column to generate an overhead stream comprising C6 compounds and lighter components, and a bottoms stream comprising heavier hydrocarbons; passing the overhead stream to a cracking unit. passing the bottoms stream to a separation unit to generate an extract stream comprising normal hydrocarbons, and a raffinate stream comprising non-normal hydrocarbons; and passing the extract stream to the cracking unit to generate light olefins.

A second embodiment of the invention is a process for increasing light olefin yields comprising passing a hydrocarbon stream to a fractionation column to generate a first overhead stream comprising nC4 and lighter hydrocarbons, and a first bottoms stream comprising C5 and heavier hydrocarbons; passing the first bottoms stream to a separation unit to generate an extract stream comprising normal hydrocarbons, and a raffinate stream comprising non-normal hydrocarbons; passing the raffinate stream to a reforming unit to generate a reformate stream; and passing the extract stream to a cracking unit to generate light olefins. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph further comprising passing raffinate stream to a raffinate separation system to generate a second overhead stream comprising C5 and C6 hydrocarbons, an intermediate stream comprising C7 and heavier alkanes, and C6 and heavier aromatics and naphthenes, and a second bottoms stream comprising desorbent.

A third embodiment of the invention is a process for providing flexibility in gasoline production passing a hydrocarbon stream to a fractionation column to generate a first overhead stream comprising nC4 and lighter hydrocarbons, and a first bottoms stream comprising C5 and heavier hydrocarbons; passing the first bottoms stream to a hydrogenation unit to generate a treated bottoms stream having a reduced acetylenes, diolefins, sulfur and nitrogen content; passing the treated bottoms stream to a separation unit to generate an extract stream comprising normal hydrocarbons, and a raffinate stream comprising non-normal hydrocarbons; passing the raffinate stream to a reforming unit to generate a reformate stream; and passing a portion of the extract stream to a cracking unit to generate light olefins. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph further comprising passing the extract stream to an extract separation system to generate a second overhead stream comprising C5 and C6 normal alkanes, an intermediate stream comprising C7 and heavier normal alkanes, and a second bottoms stream comprising desorbent.

In one embodiment, the process includes the use of an isomerization unit for converting a C5-C6 stream. The isomerization unit can be used to convert an iC5-iC6 stream to a mixture of iC5-iC6 and normal C5 and C6 components for increasing yields of light olefins. In an alternative a stream of nC5-nC6 can be passed through the isomerization unit to convert the stream to a mixture of iC5-iC6 and normal C5 and C6 components for increasing the yields for a gasoline pool.

Other objects, advantages and applications of the present invention will become apparent to those skilled in the art from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a base case showing the process of splitting a naphtha stream between a feed to a cracking unit and a feed to a reforming unit;

FIG. 2 is an embodiment showing the separation of the naphtha splitter bottoms stream to increase the light olefins yield;

FIG. 3 is an embodiment showing the separation of the naphtha splitter bottoms stream with isomerization for increasing light olefin yields; and

FIG. 4 is an embodiment showing the separation of the naphtha splitter bottoms stream with isomerization for increasing gasoline blending pool yields.

DETAILED DESCRIPTION

A process is presented for increasing the yields of light olefins or shifting to increase the hydrocarbon components to gasoline blending pools from a hydrocarbon feedstock. The process includes separating a naphtha feedstock to components to a first stream, or a cracking unit feedstream, that are more readily processed in a cracking unit and to components in a second stream, or a reforming unit feedstream, that are more readily processed in a reforming unit. The process includes the ability to convert components from the cracking stream to the reforming stream, and to convert components from the reforming stream to the cracking stream.

The processing of a naphtha feedstream can be used in the production of light olefins and providing hydrocarbon components for a gasoline blending pool or for reforming components to generate aromatic compounds to be passed to an aromatics complex. A basic process, as shown in FIG. 1, includes splitting a naphtha feedstream into two portions, a second portion 6, and a first portion 8. The amount of the second portion can be as little as zero, or can include all of the naphtha feedstream, depending on the choice of product. The second portion 6 is passed to a cracking unit 20 for generating a process stream 22 having light olefins. Light olefins include ethylene and propylene. The first portion 8 of the naphtha feedstream is passed to a naphtha splitter 10 to generate an overhead stream 12 and a bottoms stream 14. The overhead stream 12 includes C6 and lighter components in the naphtha feedstream. The bottoms stream 14 includes C6 and heavier components in the naphtha feedstream. The typical range for the heavier components is from C5 to C11 hydrocarbons. The splitter 10 operated based on the relative boiling points of the hydrocarbon components, and the splitter overhead stream 12 can comprise components that have boiling points equal to or lower than methyl cyclopentane (MCP). Operating conditions can be changed to adjust for desired overhead compositions, including changing the operating conditions to have an overhead stream 12 comprising C4 and lighter components, with the bottoms stream 14 comprising C5 and heavier components. The overhead stream 12 is passed to the cracking unit 20. The bottoms stream 14 is passed to a hydrotreating unit 30 to generate a treated stream 32. The treated stream 32 is passed to a reforming unit 40 to generate a reformate stream 42 having an increased aromatics content.

Normal components in the hydrocarbon stream are more readily cracked to form light olefins than non-normal components. The normal components are also more difficult to reform to aromatics than non-normal components. In addition, branched paraffins are preferred components for a gasoline blending pool over normal components. The separation of normal and non-normal components, combined with passing the different stream to appropriate downstream processing units improves flexibility and the economics of cracking and reforming naphtha. The ability to convert normal components to non-normal components allows the shifting of hydrocarbon components from the stream fed to a cracking unit to a stream for generating gasoline components.

In one embodiment, as shown in FIG. 2, the process is for increasing the light olefin and reformate yields. The process includes passing a first portion 8 of a hydrocarbon feedstream to a fractionation column 10 to generate an overhead stream 12 comprising C6 and lighter components, and a bottoms stream 14 comprising heavier components. The overhead stream 12 is passed to a cracking unit 20 to generate a process stream 22 that includes light olefins. The bottoms stream 14 is passed to a hydrotreating unit 30 to generate a treated bottoms stream 32. The hydrotreating unit 30 removes impurities to protect downstream catalysts and adsorbents. Impurities removed include sulfur compounds and nitrogen compounds. In addition, there can be some hydrogenation of hydrocarbon compounds, such as acetylenes and diolefins. These are more reactive compounds, and hydrogenation of these compounds can decrease some side reactions downstream, such as polymerization.

The treated bottoms stream 32 is passed to a separation unit 50 to generate an extract stream 52 and a raffinate stream 54. The separation unit 50 is preferably an adsorption separation unit, and includes an adsorbent to selectively adsorb components from the treated bottoms stream. In one embodiment, the adsorbent is selected to preferentially adsorb normal components from the stream 32, while rejecting non-normal components. The extract stream 52 comprises normal hydrocarbons in the C5 to C11 range, and the raffinate stream 54 comprises non-normal components from the bottoms stream. The non-normal components include branched paraffins, naphtenes and aromatic compounds. The extract stream 52 is passed to the cracking unit 20 to increase the light olefins yield from the hydrocarbon feedstream. In one embodiment, the hydrocarbon feedstream is a naphtha feedstream. Although the present embodiment is exemplified by a naphtha feedstream, the process is not limited to a naphtha feedstream, and can include any feedstream with a composition that overlaps with a naphtha feedstream. For a naphtha feedstream, the cracking unit 20 can be a naphtha steam cracking unit.

In one embodiment, the process further includes passing the raffinate stream 54 to a reforming unit 40 to generate a reformate stream 42 having an increased aromatics content.

The process can further include passing a second portion 6 of the hydrocarbon feedstream to the cracking unit 20.

The use of naphtha for the generation of ethylene and propylene is common It is known that normal paraffins, n-paraffins, are preferred for the relative ease of cracking over non-normal paraffins. Likewise, naphtha is used as a feedstock for reforming to generate aromatic compounds that can be used in an aromatics complex or as part of a gasoline blending pool. Non-normal paraffins are also useful components for a gasoline blending pool, or for reforming Enhancing the ability to convert a naphtha feedstock for the production of light olefins or for the production of gasoline or aromatics can enhance a refinery's economics.

In one embodiment, at shown in FIG. 3, the process provides for enhancing light olefin yields. The process includes passing a hydrocarbon feedstream 8 to a fractionation unit 10. The fractionation unit 10 generates an overhead stream 12, comprising C4 and lighter hydrocarbon components, and a bottoms stream 14 comprising C5 and heavier components. The overhead stream 12 is passed to a cracking unit 20 to generate a process stream 22 having light olefins. The bottoms stream 14 is passed to a hydrotreating unit 30 to generate a treated bottoms stream 32. The treated bottoms stream 32 is passed to a separation unit 50 to generate an extract stream 52 comprising normal hydrocarbons, and a raffinate stream 54 comprising non-normal hydrocarbons. The non-normal hydrocarbons include branched paraffins, naphthenes and aromatics. The extract stream 52 is passed to the cracking unit 20.

The raffinate stream 54 is passed to a raffinate separation system 60, and generates a raffinate overhead stream 62, an intermediate raffinate stream 64, and a raffinate bottoms stream 66. The separation unit 50 comprises an adsorption separation system, and includes using a desorbent as a working fluid in the adsorption separation process. The raffinate bottoms stream 66 comprises the desorbent and is recycled back to the separation unit 50. The intermediate raffinate stream comprises non-normal C7 to C11 paraffins, and C6 to C11 aromatic and naphthenic components in the raffinate stream. The raffinate overhead stream 62 comprises iC5 and iC6 components from the raffinate stream.

The raffinate overhead stream 62 is passed to an isomerization unit 70 to generate an isomerate stream 72. The isomerization unit 70 comprises a catalytic reactor that takes a mixture of hydrocarbon components and isomerizes the components to generate a new composition for the isomerate stream 72. The isomerization process can convert branched paraffins to normal paraffins, or can be used to convert normal paraffins to branched paraffins. In this embodiment, the feed to the isomerization unit consists of branched paraffins, and will generate a mixture of branched and normal paraffins. The isomerate stream 72 is passed to the separation unit 50. This embodiment increases the amount of normal paraffins generated and increases the feed to the cracking unit 20. The increase feed of normal paraffins to the cracking unit increases the amount of light olefins generated for the cracking process stream 22.

In one embodiment, as shown in FIG. 4, the process provides for flexibility to increase gasoline production, or to increase aromatics production. The process includes passing a hydrocarbon feedstream 8 to a fractionation unit 10. The fractionation unit 10 generates an overhead stream 12, comprising C4 and lighter hydrocarbon components, and a bottoms stream 14 comprising C5 and heavier components. The overhead stream 12 is passed to a cracking unit 20 to generate a process stream 22 having light olefins. The bottoms stream 14 is passed to a hydrotreating unit 30 to generate a treated bottoms stream 32. The treated bottoms stream 32 is passed to a separation unit 50 to generate an extract stream 52 comprising normal hydrocarbons, and a raffinate stream 54 comprising non-normal hydrocarbons. The non-normal hydrocarbons include branched paraffins and olefins, naphthenes and aromatics.

The raffinate stream 54 is passed to a raffinate separation system 60, and generates a raffinate overhead stream 62, an intermediate raffinate stream 64, and a raffinate bottoms stream 66. The separation unit 50 comprises an adsorption separation system, and includes using a desorbent as a working fluid in the adsorption separation process. The raffinate bottoms stream 66 comprises the desorbent and is recycled back to the separation unit 50. The intermediate raffinate stream comprises non-normal C7 to C11 paraffins and C6 to C11 aromatic and naphthenic components in the raffinate stream. The raffinate overhead stream 62 comprises iC5 and iC6 components from the raffinate stream, which can then be passed to a gasoline blending pool, or other desired downstream process.

The extract stream 52 is passed to an extract separation system 80, and generates an extract overhead stream 82, an intermediate extract stream 84, and an extract bottoms stream 86. The extract bottoms stream 86 comprises desorbent and is recycled to the adsorption separation unit 50. The extract intermediate stream 84 comprises C7 to C11 normal paraffins and is passed to the cracking unit 20 to generate light olefins.

The extract overhead stream 82 comprises nC5 and nC6 paraffins, and is passed to the isomerization unit 70 to generate an isomerization process stream 72. The isomerization process stream 72 is passed to the separation unit 10 to convert a stream of normal paraffins to a mixture of normal and branched paraffins. This embodiment increases the amount of branched paraffins and increases the amount of raffinate from the separation unit 10. This provides an increase in iC5 and iC6, and results in an increase in the raffinate overhead stream 62, or an increase in the feed to a gasoline blending pool.

The extract separation system and/or the raffinate separation system can comprise one or more fractionation columns for separating the respective extract or raffinate stream into multiple streams. Options for the extract separation and/or raffinate separation system include divided wall columns or other means for separating hydrocarbon streams.

The addition of the separation unit 10 can be seen in the following results, wherein there is a substantial increase in the normals content and aromatics content. This promotes the increase of light olefins for cracking. The addition of isomerization also show that one can increase the normals and aromatics. This provides a useful enhancement of existing facilities.

TABLE Comparison of Cases Description % normals N + 2A Case 1 Base case - no separation unit 26 57 Case 2 With separation unit 59 71 Case 3 With separation and isomerization 94 73

Case 1 provides a comparison of the standard processing used in industry today, wherein a straight run naphtha is fed to a steam cracker with a minimum of preparation. The straight run naphtha may be combined with light ends from a separate naphtha stream that is being process for a catalytic reforming unit. The normals in the naphtha are typically in the 15% to 30% by weight range. With the addition of the separation unit, the separation can increase the amount of normals, as shown in case 2, for the feed to the cracking unit. The addition of the isomerization unit allows for further improvement in the quality of feeds to the cracking unit, and to the reforming unit. The quality of the feed to the reforming unit (N+2A, or aromatic potential) shows that the treatment improves yields from the reforming unit.

The addition of the isomerization unit also allows for more flexibility by allowing a plant operator to control the feeds to either the cracking unit or the reforming unit, but shifting the quality of the hydrocarbon stream. The isomerization unit allows of increasing either the amount of normal, or the amount of branched paraffins, in the form of iC5 and iC6.

While the invention has been described with what are presently considered the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. 

1. A process to increase light olefin and reformate yields, comprising: passing a first portion of a hydrocarbon feedstream to a fractionation column to generate an overhead stream comprising C6 compounds and lighter components, and a bottoms stream comprising heavier hydrocarbons; passing the overhead stream to a cracking unit. passing the bottoms stream to a separation unit to generate an extract stream comprising normal hydrocarbons, and a raffinate stream comprising non-normal hydrocarbons; and passing the extract stream to the cracking unit to generate light olefins.
 2. The process of claim 1 wherein the hydrocarbon feedstream is a naphtha.
 3. The process of claim 1 further comprising: passing the bottoms stream to a hydrotreating unit to generate a treated bottoms stream; and passing the treated bottoms stream to the separation unit.
 4. The process of claim 1 wherein the separation unit is an adsorption separation unit.
 5. The process of claim 1 further comprising passing the raffinate stream to a reforming unit to generate a reformate stream comprising aromatics.
 6. The process of claim 1 further comprising passing a second portion of the hydrocarbon feedstream to the cracking unit.
 7. The process of claim 1 wherein the cracking unit is a naphtha steam cracking unit.
 8. A process for increasing light olefin yields comprising: passing a hydrocarbon stream to a fractionation column to generate a first overhead stream comprising nC4 and lighter hydrocarbons, and a first bottoms stream comprising C5 and heavier hydrocarbons; passing the first bottoms stream to a hydrotreating unit to generate a treated bottoms stream; passing the treated bottoms stream to a separation unit to generate an extract stream comprising normal hydrocarbons, and a raffinate stream comprising non-normal hydrocarbons; passing the raffinate stream to a reforming unit to generate a reformate stream; and passing the extract stream to a cracking unit to generate light olefins.
 9. The process of claim 8 wherein the hydrotreating unit generates a treated first bottoms stream having a reduced acetylenes, diolefins, sulfur and nitrogen content.
 10. The process of claim 9 wherein the hydrotreating unit is a naphtha hydrotreating unit.
 11. The process of claim 8 wherein the hydrocarbon stream comprises a naphtha.
 12. The process of claim 8 further comprising passing raffinate stream to a raffinate separation system to generate a second overhead stream comprising C5 and C6 hydrocarbons, an intermediate stream comprising C7 and heavier alkanes, C6 and heavier aromatics and naphthenes, and a second bottoms stream comprising desorbent.
 13. The process of claim 12 further comprising passing the intermediate stream to the reforming unit.
 14. The process of claim 12 further comprising passing the second overhead stream to an isomerization unit to generate an isomerization process stream comprising isoparaffins and normal paraffins.
 15. The process of claim 14 further comprising passing the isomerization process stream to the separation unit.
 16. A process for providing flexibility in gasoline production: passing a hydrocarbon stream to a fractionation column to generate a first overhead stream comprising nC4 and lighter hydrocarbons, and a first bottoms stream comprising C5 and heavier hydrocarbons; passing the first bottoms stream to a hydrogenation unit to generate a treated bottoms stream having a reduced acetylene and diolefins content; passing the treated bottoms stream to a separation unit to generate an extract stream comprising normal hydrocarbons, and a raffinate stream comprising non-normal hydrocarbons; passing the raffinate stream to a reforming unit to generate a reformate stream; and passing a portion of the extract stream to a cracking unit to generate light olefins.
 17. The process of claim 16 further comprising passing the extract stream to an extract separation system to generate a second overhead stream comprising C5 and C6 normal alkanes, an intermediate stream comprising C7 and heavier normal alkanes, and a second bottoms stream comprising desorbent.
 18. The process of claim 17 further comprising passing the second overhead stream to an isomerization unit to generate an isomerization process stream.
 19. The process of claim 18 further comprising passing the isomerization process stream to the separation unit.
 20. The process of claim 17 further comprising passing the intermediate stream to the cracking unit. 